Filter arrangement

Abstract

The invention relates to a filter arrangement having a local oscillator ( 4 ), having two band-pass filters ( 1, 2 ) and having a mixer ( 3 ). The novel filter arrangement distinguishes itself in that two band-pass filters ( 1, 2 ) having the same bandwidth f B and center frequency f c have been provided, the first band-pass filter ( 1 ) having its output coupled to the input of the second band-pass filter ( 2 ) by means of a mixer ( 3 ), and the local oscillator ( 4 ) is adapted to control the mixer ( 3 ).

1 . A filter arrangement having a local oscillator( 4 ), having band-pass filters ( 1 ,  2 ) and having a mixer ( 3 ), 
 characterized in that 
 two band-pass filters ( 1 ,  2 ) having the same bandwidth f B  and center frequency f c  have been provided, the first band-pass filter ( 1 ) having its output coupled to the input of the second band-pass filter ( 2 ) by means of a mixer ( 3 ), and the local oscillator ( 4 ) is adapted to control the mixer ( 3 ).  
   
     
     
         2 . A filter arrangement as claimed in  claim 1 , 
 characterized in that 
 the frequency of the output signal (F 3 ) of the local oscillator ( 4 ) is variable and the bandwidth f B  and the center frequency f c  of the output signal (F 2 ) of the filter arrangement is varied by changing the frequency of the output signal (F 3 ) of the local oscillator ( 4 ).  
   
     
     
         3 . A filter arrangement as claimed in  claim 2 , 
 characterized in that 
 it is adapted to select the intermediate frequency in the case of quadrature amplitude modulation.  
   
     
     
         4 . A filter arrangement as claimed in  claim 1 , 
 characterized in that 
 the band-pass filters ( 1 ,  2 ) have a fixed bandwidth f B .